It has been widely known that limulus amoebocyte lysate (hereinafter referred to as LAL) reacts with an endotoxin which is a bacterial pyrogen (hereinafter referred to as endotoxin) to cause a coagulation.
On the basis of this reaction, various methods of assaying endotoxin have been developed.
Recently, the above-described coagulation reaction mechanism has been elucidated, i.e., coagulogen is converted to coagulin to cause a coagulation (gelation) according to a stepwise reaction as shown in FIG. 1 [S. Iwanaga et al., The hemolymph coagulation system in invertebrate animals, J. Protein Chem., 5, 255-268 (1986)]. It can be understood that the reaction mechanism includes two coagulation systems: a system initiated by endotoxin (factor C system) and a system initiated by (1.fwdarw.3)-.beta.-D-glucan (e.g., curdlan, partially carboxyfnethylated (1.fwdarw.3)-.beta.-D-glucan) (factor G system).
The present inventors already found that the (1.fwdarw.3)-.beta.-D-glucan structural portion having a particular molecular weight inhibits the activation of the system of LAL initiated by (1.fwdarw.3)-.beta.-D-glucan (factor G system), and filed the patent application as a limulus amoebocyte lysate factor G activation inhibitor (Japanese Patent Application No. 63-216341 and WO 90/02951).
However, when this inhibitor is added to LAL in order to obtain LAL specific to endotoxin, a complex comprising the inhibitor and factor G remaining in LAL is possibly dissociated with a sample added and the liberated factor G is activated by a factor G-activating substance.